1. Field of the Invention
The present invention relates to a driving force transmission apparatus, a method for producing this apparatus, and an extendible structure with the driving force transmission apparatus. More particularly, the present invention relates to a light driving force transmission apparatus which may transmit a driving force without use of friction and with high lubrication, to a method for producing this light driving force transmission apparatus, and to an extendible structure provided with this light driving force transmission apparatus applicable for example in space environment.
2. Description of the Related Background Art
As driving force transmission means for transmitting a driving force, transmission wheels of driving and driven wheels directly contacting each other and sprocket wheels or belt wheels transmitting a driving force through a chain or a belt are known.
The driving force transmission by the chain and sprockets requires periodical supply of grease or lubricant upon maintenance of apparatus to maintain lubrication of contacting portions. The driving force transmission by the wire rope and pulleys requires holding of proper friction because the driving force is transmitted from the pulley to the wire through a frictional force between the parts.
If such driving force transmission apparatus is used in space environment, lubrication becomes a great problem. For example, the sprockets cannot be dipped in a lubricant in vacuum, and it is also difficult to maintain the wire rope in a proper stretch state, which makes a sufficient friction unobtainable.
A so-called ball chain has been proposed, in which beads or balls of resin are attached as connection members at a predetermined pitch onto a wire rope, and in which sprockets are provided with recesses connected to the connecting members of beads or balls. Reference is made regarding to such ball chains to Japanese Unexamined Patent Publication Sho 62-268857 and Japanese Examined Patent Publication Sho 61-16686. Such a ball chain enables rotation at a uniform rate to assure a proper frictional force without fine adjustment of the chain tension.
However, the above-described ball chain is intended to accurately transmit rotation of a driving wheel to a driven wheel, but not to transfer an object utilizing the rotation of ball chain. Thus the ball chain cannot be used as a transfer mechanism.
The balls must be positioned with high precision on the ball chain in order to accurately rotate the ball chain. It is in general known that the precision is poor for attachment of ball connection members to the wire rope. More specifically, the ball chain is obtained by consecutive caulking of caulking members which are positioned at specific positions starting from one end to the other end of the wire rope. The caulking is carried out after measurement of the position from a preceding caulking member already caulked on the wire rope. Such measurement and caulking are repeated one by one on the wire rope. Therefore, it is tedious and complex to complete the caulking of all caulking members on the wire rope. In addition, the precision of the ball chain is lowered by accumulation of dimensional errors between the caulking members.
An application of such a driving force transmission apparatus is used in space environment. There is proposed an extendible structure which expands and supports in space an antenna reflector or a solar battery paddle stored in a part of space station (see 31ST AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, AIAA-90-1054, Development of a High Stiffness Extendible and Retractable Mast `HIMAT` for Space Applications).
The extendible structure provides a complete structure system by extending a mast of truss structure stored in a canister by means of a raising drive mechanism. In order to extend such a conventional extendible structure, projections are provided at apexes of a truss structure member to be moved in a specific direction by using the rotation of rotating grooves of screw jacks in the raising drive mechanism.
The rotation of a motor is distributed to the respective screw jacks in the raising drive mechanism by a timing belt to drive them, creating a problem of complicated structure.
Further, since the screw jack itself is considerably heavy, the weight of extendible structure inevitably increases, which is fatal for a space station most importantly requiring weight reduction.